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Abstract

A Near Infrared Spectral Tomography (NIRST) system has been developed and integrated into a commercial Digital Breast Tomosynthesis (DBT) scanner to allow structural and functional imaging of breast in vivo. The NIRST instrument uses an 8-wavelength continuous wave (CW) laser-based scanning source assembly and a 75-element silicon photodiode solid-state detector panel to produce dense spectral and spatial projection data from which spectrally constrained 3D tomographic images of tissue chromophores are produced. Integration of the optical imaging system into the DBT scanner allows direct co-registration of the optical and DBT images, while also facilitating the synergistic use of x-ray contrast as anatomical priors in optical image reconstruction. Currently, the total scan time for a combined NIRST-DBT exam is ~50s with data collection from 8 wavelengths in the optical scan requiring ~42s to complete. The system was tested in breast simulating phantoms constructed using intralipid and blood in an agarose matrix with a 3 cm x 2 cm cylindrical inclusion at 1 cm depth from the surface. Diffuse image reconstruction of total hemoglobin (HbT) concentration resulted in accurate recovery of the lateral size and position of the inclusion to within 6% and 8%, respectively. Use of DBT structural priors in the NIRST reconstruction process improved the quantitative accuracy of the HbT recovery, and led to linear changes in imaged versus actual contrast, underscoring the advantages of dual-modality optical imaging approaches. The quantitative accuracy of the system can be further improved with independent measurements of scattering properties through integration of frequency or time domain data.

(a) Schematic of the intralipid/blood inclusion phantom construct which is 24 cm (in the X-direction) by 16 cm (in the Y-direction) by 5.2 cm (in the Z-drection). (b) Photographs of the fabricated top and bottom layers of the phantom and the addition of a liquid inclusion.

X-Y cross-sectional views of the reconstructed HbT images for the 1:1 (a), 2:1 (b), and 3:1 (c) contrast phantoms. (d) Cut-away view of the FEM mesh showing the background and inclusion regions. (e) Plot of recovered HbT contrast in the background (solid triangles) and inclusion region (solid circles) vs actual HbT concentration in the background and inclusion. Linear fits show that the HbT concentration is nearly constant in the background and varies linearly in the inclusion as expected.